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Andrea Smith, Richard Clark, and Richard Jeffries
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Russell L. Elsberry and Richard A. Jeffries

Abstract

Vertical wind shears between 200 and 850 mb are calculated from operational analyses and special interactive analyses for Tropical Storm Steve during the Tropical Cyclone Motion (TCM-93) field experiment and for Typhoon Omar at the end of the TCM-92 experiment. The operational Fleet Numerical Meteorology and Oceanography Center (FNMOC) analyses have strong 200-mb winds crossing over the intensifying storms, which leads to vertical wind shears exceeding the 12.5 m s−1 threshold value believed to prevent tropical cyclone intensification. Interactive analyses are produced with the multiquadric interpolation technique that blends composited cloud-drift winds and aircraft reports between 1800 and 0000 UTC and between 0600 and 1200 UTC, sets of synthetic observations to represent missing or mislocated tropical circulations, and the FNMOC analyses that are used as a first-guess field. These interactive analyses indicate that the high winds at 200 mb associated with low-latitude circulations such as monsoon depressions or other tropical cyclones that appear to be impinging on Steve and Omar are actually deflected around the convective outflows. Vertical wind shears calculated from the interactive analyses are well below the threshold vertical wind shear value, which is consistent with the observed intensification of Steve and Omar. In seven of the nine Steve analyses, the insertion of the composite observations alone resulted in deflected flow around convective outflow, so that the reduced shears are not an artifact of synthetic observation insertions. It is hypothesized that the large vertical wind shears associated with the low-latitude circulations may actually be concentrated in a shallow layer that may be opposed and deflected by a similar shallow layer of convective outflow above developing and intensifying tropical cyclones. In that case, an understanding of the role of vertical wind shear and prediction of tropical cyclone intensification may require special analyses of the type developed following the TCM-93 experiment.

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James S. Goerss and Richard A. Jeffries

Abstract

In June 1990, the assimilation of synthetic tropical cyclone observations into the Navy Operational Global Atmospheric Prediction System (NOGAPS) was initiated at Fleet Numerical Oceanography Center (FNOC). These observations are derived directly from the information contained in the tropical cyclone warnings issued by the Joint Typhoon Warning Center (JTWC) and the National Hurricane Center. This paper describes these synthetic observations, the evolution of their use at FNOC, and the details of their assimilation into NOGAPS. The results of a comprehensive evaluation of the 1991 NOGAPS tropical cyclone forecast performance in the western North Pacific are presented. NOGAPS analysis and forecast position errors were determined for all tropical circulations of tropical storm strength or greater. It was found that, after the assimilation of synthetic observations, the NOGAPS spectral forecast model consistently maintained the tropical circulations as evidenced by detection percentages of 96%, 90% and 87% for 24-, 48-, and 72-h forecasts, respectively. The average forecast position errors were 188, 299, and 434 km for the respective forecasts. The respective errors for the One-Way Influence Tropical Cyclone Model (OTCM), one of JTWC's primary track-forecasting aids, were 215, 364, and 529 km. In homogeneous comparisons the percent improvement of the NOGAPS 48- and 72-h forecasts was 14% and 12% over the OTCM and 31% and 33% over JTWC's operational Climatology–Persistence Model.

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Victoria Johnson, Richard Jeffries, Greg Byrd, Wendy Schreiber-Abshire, Elizabeth Page, Bruce Muller, and Tim Alberta

Abstract

The Cooperative Program for Operational Meteorology, Education, and Training (COMET)’s mission when it began in 1990 was to deliver professional development opportunities to U.S. government forecasters during the National Weather Service (NWS) modernization program. Since then, COMET has emerged as a worldwide leader in geoscience education. Its original objectives were to provide forecasters with classroom and distance learning training based on state-of-the-art science; support development and testing of new forecast methods; promote collaboration between the forecasting, research, and academic communities; and to advance forecasting and nowcasting by encouraging research. Over the years, COMET’s mission has expanded to disseminating and enhancing scientific knowledge in the environmental sciences, particularly meteorology, but also including diverse areas such as oceanography, hydrology, space weather, and emergency management. This paper reviews COMET’s evolution from a primary focus on educating U.S. forecasters on the application of new technologies (such as Doppler radar) to mesoscale meteorology problems into a program with a much broader scope. Those changes include offering learning opportunities that now cover a wider variety of topics and support the educational needs of diverse audiences worldwide. The history of COMET is a story of adaptation to technological changes, funding cycles, partner requirements, and service opportunities as well as taking on a more global mission. We will look at how COMET’s activities in geoscience education have changed, how its adaptability has contributed to the longevity of the program that was only supposed to exist until the NWS modernization was complete, and expectations and plans for the future.

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Charles P. Guard, Lester E. Carr, Frank H. Wells, Richard A. Jeffries, Nicholas D. Gural, and Dianne K. Edson

Abstract

The Joint Typhoon Warning Center (JTWC), a specialized component of the Naval Oceanography Command Center, Guam, is the busiest tropical cyclone warning center in the world. Its area of responsibility encompasses four broad oceanic areas of tropical cyclone activity stretching from the international date line to the east coast of Africa, in both hemispheres. Our paper discusses the challenges imposed on the center as a result of its vast multibasin area of responsibility, the products the center produces, its warning philosophy, observational networks, analysis and forecast schemes, and the military aspects of the operation. Because of the multibasin, dual-hemisphere responsibility, there is no off-season. The challenges of information and time management, analysis and forecast improvement, expansion of meteorological understanding, and enhancement of the warning process are discussed. Current methods used to meet these challenges are presented. In addition, the paper gives a brief overview of JTWC's colorful history, with emphasis on the aircraft reconnaissance era and the evolution of satellite reconnaissance. The joint Navy-Air Force Operations Evaulation to assess the impact of the loss of aircraft reconnaissance and the Office of Naval Research Tropical Cyclone Motion-90 Experiment are briefly discussed. Finally, the paper takes a cursory look at JTWC's postanalysis program, which includes the Annual Tropical Cyclone Report; training, qualification, and certification programs; and technique development to improve tropical cyclone analysis and forecasting.

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Roger Edwards, Stephen F. Corfidi, Richard L. Thompson, Jeffry S. Evans, Jeffrey P. Craven, Jonathan P. Racy, Daniel W. McCarthy, and Michael D. Vescio

Abstract

Forecasters at the Storm Prediction Center (SPC) were faced with many challenges during the 3 May 1999 tornado outbreak. Operational numerical forecast models valid during the outbreak gave inaccurate, inconsistent, and/or ambiguous guidance to forecasters, most notably with varying convective precipitation forecasts and underforecast wind speeds in the middle and upper troposphere, which led forecasters (in the early convective outlooks) to expect a substantially reduced tornado threat as compared with what was observed. That, combined with relatively weak forecast and observed low-level convergence along a dryline, contributed to much uncertainty regarding timing and location of convective initiation. As a consequence, as the event approached, observational diagnosis and analysis became more important and were critical in identification of the evolution of the outbreak. Tornadic supercells ultimately developed earlier, were more numerous, and produced more significant tornadoes than anticipated. As forecasters addressed the meteorological facets of the tornadic storms on the evening of 3 May 1999, there were other areas of simultaneous severe-storm development, and one of the tornadoes posed a threat to the facility and family members of the forecast staff. These uncertainties and challenges are discussed in the context of SPC convective outlooks and watches for this outbreak. Recommendations are made for continued research aimed at improving forecasts of convective initiation and mode.

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